Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically use various techniques, such as layering, doping, masking, and etching, to build thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
Interconnecting millions of microscopic components typically entails covering the components with an insulative layer of silicon dioxide, etching small holes in the insulative layer to expose portions of the components underneath, and digging trenches in the layer to define a wiring pattern. Then, through metallization, the holes and trenches are filled typically with aluminum, to form line-like aluminum wires between the components. The aluminum wires are typically about one micron thick, or about 100 times thinner than a human hair.
Silicon dioxide and aluminum are the most common insulative and conductive materials used to form interconnections today. However, at sub-micron dimensions, that is, dimensions appreciable less than one micron, aluminum and silicon-dioxide interconnection systems present higher electrical resistances and capacitances which waste power and slow down integrated circuits. Moreover, at these smaller dimensions, aluminum exhibits poor electromigration resistance, a phenomenon which promotes disintegration of the aluminum wires at certain current levels. This ultimately undermines reliability, not only because disintegrating wires eventually break electrical connections but also because aluminum diffuses through surrounding silcon-dioxide insulation to form short circuits with neighboring wires. Thus, at submicon dimensions, aluminum and silicon-dioxide interconnection systems waste power, slow down integrated circuits, and compromise reliability.
Copper appears, because of its lower electrical resistivity and higher electromigration resistance to be a promising substitute for aluminum. And, many polymers, for example, fluorinated polyimides, because of their lower dielectric constants, appear to be promising substitutes for silicon dioxide. Thus, a marriage of copper with these polymers promises to yield low-resistance, low-capacitance interconnective structures that will improve the efficiency and speed of integrated circuits.
Unfortunately, copper reacts with these polymers to form conductive copper dioxide within these polymers, reducing their effectiveness as low-capacitance insulators and ultimately leaving the copper-polymer promise of superior efficiency and speed unfulfilled.